The present invention relates to a reversal process for producing negative copies by means of a normally positive-working light-sensitive material based on 1,2-quinone diazides.
It is known that positive-working reproduction materials based on 1,2-naphthoquinone diazides can be negatively processed by a particular sequence of treatment steps. In U.S. Pat. No. 3,264,104, a reversal process of this kind is described in which the light-sensitive layer, which preferably contains thermoplastic polymers, is imagewise exposed, is treated with an alkaline solution or with water (if appropriate, at an elevated temperature) without washing off the exposed areas in the process, is then exposed again without an original, and finally is developed in a conventional manner, such that the originally imagewise exposed areas remain on the support and the other areas are washed off.
This process has the disadvantages that a comparatively large number of treatment steps are required; that the first treatment with alkali must invariably be carried out with particular care, in order to detach as little as possible of the exposed layer, which is soluble in aqueous alkali; and that it is necesary to add polymers which are sparingly soluble in alkali and which limit the applicability of the material to other uses.
European Patent Application No. 0,024,916 discloses a similar reversal process for the production of resist layers, in which a photosensitive material based on 1,2-quinone diazides is heated after imagewise exposure, then exposed again without an original and developed with an aqueous alkaline solution to form a negative. The light-sensitive layer of the disclosed material contains particular photochromic compounds which react with the products of the photoreaction undergone by the quinone diazide with heating of the material, and are stated to effect curing of the layer. In this material, photochromic substances must be present, the photoreaction of which produces a discoloration which is inconvenient in some applications.
British Patent Application No. 2,082,339 describes a light-sensitive composition comprising an o-quinone diazide and at least one resol, for use in the manufacture of a lithographic printing plate which is suitable for both positive and negative processing. This reversal process covers the same sequence of steps as the process disclosed by the aforementioned European patent application. The reversal action is based on the fact that the photodecomposition products of the o-quinone diazide form an insoluble reaction product with the resol, under the action of heat. A reaction of this kind does not occur if novolaks are used. The printing plates so produced have the disadvantage of a relatively poor shelf-life, due to the self-curing character of resols.
In German Offenlegungsschriften Nos. 2,855,723 and 2,529,954 resist layers comprising 1,2-quinone diazides are described, which layers are used for a reversal process and contain, in addition, N-acyl-N'-methylol-ethylenediamines or hydroxyethylimidazoles to effect thermal curing of the layer. A similar material comprising secondary or tertiary amines is described in U.S. Pat. No. 4,196,003.
Additives of the kind mentioned above, however, generally have an adverse influence on the shelf-life of the copying layers and on specific properties relating to copying technique, such as, for example, sensitivity to light and image contrast after exposure.